Well unlike everyone else who says to just play bear I guess I'll tell you what to do if you are boss tanking Gul'dan as a warrior. Our comp is Warrior/Druid and we have our warrior tanking the boss because our druid is terrible at CD management. We are also still progressing but are in second phase going into 3rd.
Every scythe you need to have spell reflect for, and 1-2 additional effects depending on strength. I also had to save my immunity for the Fel Lord's second shatter so that was not an option for me to use on scythes. I'd typically use these following combos for scythe:
SR/DS/Ironbark
SR/DS/Trinket
SR/DS/LS
SR/SW
We haven't had our holy paladin in because of computer issues so I'd have a sacrifice somewhere in there too at some point ideally. I will also use nelth's fury sometimes during it (not because it blocks the scythe) just so I won't spike to any melees during the scythe. You have to run anger management to have these CDs up each time for the scythes, no way around it. If you need visual help here
I'll link a short vod of our P1 as well.
Edit: As far as gear goes, I'm probably a little overkill on Versatility to be honest. I'm at 20% (10% DR). My armory should be up to date with what I am wearing since I'm not swapping out of it during raid nights.